1. Field of the Invention
The present invention particularly relates to a method and apparatus for producing hydrogen using waste silicon as a raw material, and an engine employing hydrogen production apparatus.
2. Description of the Related Art
Conventionally, hydrogen is mainly produced using natural gas as the raw material. More specifically, natural gas is subjected to steam reforming reaction to produce hydrogen and carbon monoxide. Further, by carrying out water gas shift reaction between carbon monoxide and water vapor, the produced gases are transformed into hydrogen and carbon dioxide. The hydrogen and carbon dioxide are then separated by membrane separation to obtain pure hydrogen. In other known methods, hydrogen is produced as a coke oven gas during iron fabrication or as a by-product generated during manufacture of caustic soda. Furthermore, it is also possible to produce hydrogen using solar cell, wind power, or biomass.
For example, Japanese Patent Laid-Open Publication No. Hei 8-115733 discloses producing hydrogen by arranging, in water, a heat-resistant electrode in contact with a reactive metal member, which may be an aluminum member or a magnesium member, that undergoes an electrothermal chemical reaction with water. Using this arrangement, electricity is conducted through the reactive metal member and the heat-resistant electrode to perform underwater electric discharge, so as to produce hydrogen by the electrothermal chemical reaction between the reactive metal member and water.
Japanese Patent Laid-Open Publication No. Hei 10-208755 describes generating hydrogen by allowing a catalyst to contact water heated to 100° C. or below, so as to decompose water.
Despite the above methods, there still exists a need for a technique which realizes stable mass production of hydrogen at a low cost, in light of the forthcoming age of full cells requiring much more hydrogen production.
In recent years, a hydrogen production method which is more inexpensive than conventional methods has been proposed. According to this method, silicon and an alkali liquid are reacted to generate hydrogen.
For example, Japanese Patent Laid-Open Publication No. 2000-191303 discloses a hydrogen production apparatus in which scrap silicon from a semiconductor device manufacturing line is ground into particles having a diameter between several ten to several hundred μm, the pH level of an alkali drain liquid from a semiconductor device manufacturing line is adjusted, and the scrap silicon and the alkali drain liquid are subsequently reacted at 50° C. or above.
Japanese Patent Laid-Open Publication No. 2001-213609 describes a hydrogen production method in which, in order to prevent generation of a violent reaction immediately after the contact between silicon and an alkali liquid, silicon and water are mixed to form a slurry in advance, and the silicon slurry and an alkali liquid are subsequently reacted. It is disclosed that, according to this method, hydrogen gas having a maximum hydrogen pressure of approximately 0.2 MPa can be obtained.
In a silicon wafer manufacturing process, semiconductor products are fabricated by cutting and polishing monocrystalline silicon. The fabrication yield is limited to about 20-25%, consequently generating a large amount, namely, 75-80%, of silicon as waste silicon powder in a slurry state. Typically, the composition of the waste silicon powder is approximately 90% high-purity silicon and approximately 10% silicon oxide. Very recently, as disclosed in the specification of Registered Japanese Patent No. 3316484, it became possible to continuously separating silicon cakes from drain water containing the waste silicon powder.
It is therefore desired to provide a method and apparatus for reusing the separated silicon cakes.
Further, as explained above, there exists a need for a low-cost hydrogen production method.